The National Institute of Mental Health Research Domain Criteria (RDoC)
"Circadian Rhythms are endogenous self-sustaining oscillations that organize the timing of biological systems to optimize physiology and behavior, and health. Circadian Rhythms:
- Are synchronized by recurring environmental cues;
- Anticipate the external environment;
- Allow effective response to challenges and opportunities in the physical and social environment;
- Modulate homeostasis within the brain and other (central/peripheral) systems, tissues and organs;
- Are evident across levels of organization including molecules, cells, circuits, systems, organisms, and social systems."